Hubble images show blob of water vapor near Europa’s south pole.

Just a few days ago, we covered a study investigating possible circulation patterns in the subsurface ocean of Jupiter’s moon Europa that could help explain its surface features. That ocean is back in the news already, because the Hubble Space Telescope might have caught a glimpse of some of its water—being sprayed high above Europa’s icy surface.

Europa and Saturn’s moon Enceladus share so many traits that the casual observer could be excused for confusing the two. Both have smooth, icy shells interrupted by fascinating wrinkles, with properties that hint at a subsurface ocean. This latest finding appears to add another similarity to the list. Enceladus hosts beautiful and distinctive jets of H2O that erupt from cracks in its southern hemisphere and form one of Saturn’s myriad rings.

Researchers were curious if something similar could be found on Europa, but, unlike Enceladus, it does not have a spacecraft in its neighborhood taking close-up pictures. So a team of researchers led by Lorenz Roth and Joachim Saur at the University of Cologne pointed the Hubble Space Telescope at it in November and December of last year.

Looking for something as small and ethereal as a spray of water with Hubble isn’t as simple as snapping a photo and taking a gander at it. The researchers looked at the light collected by the telescope at UV wavelengths associated with the O2, O, and H2O molecules known to be present in Europa’s very sparse atmosphere. After removing background noise, they also had to remove the light reflected by Europa’s bright surface. What’s left is light emitted by atmospheric gases.

Of the two observations—one in early November and one in late December—the later one showed an interesting blob of water vapor near Europa’s south pole. Doing some computer modeling, the researchers show that the observations are best explained by two plumes of water vapor propelled as much as 200 kilometers above the surface.

Why would they be seen in the December data but not the November observations? One other observation that dates from 1999 would have been capable of detecting this water as well, but it did not. An explanation may come via an analogy to those other geysers. Back in July, we covered a study showing that the jets on Enceladus ebb and flow as it orbits Saturn. Because Enceladus is a little farther from Saturn at one end of its elliptical orbit, it experiences gravitational squeezing that can affect the outlets of the jets.

The same thing could be happening on Europa. Consistent with the way this would be expected to work, the image with the plume was taken when Europa was close to its orbit's farthest point from Jupiter. The other two images, in which no plume was apparent, were taken when it was near its closest point. If these plumes were coming out of fractures in Europa’s icy shell, those polar fractures are more likely to be pulled apart when Europa is farther from Jupiter.

The limited imagery we have of Europa may not be much help in confirming the existence of these plumes, though some of that material must settle back to the surface, which might be easier to spot. Unlike the questions about how water circulates in Europa’s ocean, we’ve got a chance at learning about these plumes without having to drill through Europa’s icy armor.

Promoted Comments

So does this mean it's theoretically possible to shoot a probe through a plume, scoop up some water, and analyze it for organic substances? Seems like Europa is offering a sample without the need to drill into it.